The invention is directed to an improved method and apparatus of imparting accurate, reliable, and selective pressures on components during picking and placing thereof. In particular, the invention is directed to a method and apparatus of picking up a component from a supply surface and placing the component onto a substrate surface and applying pressures selectively to the component when it is sandwiched between a tool and either of the supply or substrate surfaces.
In this regard, the reader's attention is directed to U.S. Pat. No. 4,611,397--PICK AND PLACE METHOD AND APPARATUS FOR HANDLING ELECTRICAL COMPONENTS--Janisiewicz, et al, issued Sept. 16, 1986, and the disclosure thereof is incorporated herein by reference, since the instant invention is particularly applicable to the subject matter thereof.
The apparatus of the above-mentioned patent provides an inner spindle telescopic within an outer spindle, with the pressure experienced by a component during sandwiching thereof between a surface and the tip of the inner spindle being sensed according to telescoping of the spindles and compression of a spring between the inner spindle and a load cell. The apparatus of this earlier patent experienced contamination of internal bearing surfaces with dirt drawn in between the inner and outer spindles by the vacuum applied to the spindles. The vacuum also created an additional compressive force against the load cell which could not be counteracted. Also, erratic readings and poor placement pressure accuracies are directly attributable to sensitivity of the load cell to temperature and vibration. The compression spring typically had a spring constant with a plus or minus 20 percent margin of error so as to be very unreliable. Still further, this prior art device was not adapted to compensate for binding which can occur when the actuator drive and the longitudinal axis of the spindle assembly become slightly out of parallel from wear or tolerances, resulting in poor actuator movement.
Accordingly, it is the object of the instant invention to improve the reliability and accuracy and selectivity of pick and place pressures, particularly when dealing with a component commonly referred to as a surface mountable component (SMC).
It is another object of the invention to reduce placement force tolerances to within plus or minus 10 percent throughout a range of about 3.5 to about 50 pounds per square inch.
It is another object of the invention to obviate the earlier described pick and place pressure unreliabilities caused by compression spring tolerances.
It is also an object of the invention to obviate inaccurate pressure readings due to additional compressive forces being applied to a load cell or the like by the vacuum by which the component is held.
It is also an object of the invention to eliminate or obviate dirt contamination of bearing surfaces as caused by vacuum drawing in dirt between the inner and outer spindles.
It is a further object of the invention to obviate potential "binding" caused by a spindle axis and a drive axis being slightly unparallel.
Still further, an object of this invention is to improve the accuracies of orientation of a component about the Z-axis during rotation of the vacuum spindle thereabout.